In 1982, I was a sergeant in charge of a "front line" community policing team in Brixton. The locals actively helped us when we were chasing robbers, but we had doors slammed in our faces when chasing cannabis smokers.

Different communities tolerate different types and levels of criminality. If you want community support for policing, you must concentrate on the crimes at the top of the community's list. In Lambeth, crack cocaine, heroin and street robbery were at the top; cannabis was nowhere to be seen. Some even saw cannabis as an excuse for officers to stop, search and criminalise young people. Everyone saw the difference between "hard" and "soft" drugs in terms of policing priorities.

A month before I arrived in Lambeth, Brixton Constable Ross Callaghan failed a targeted "integrity test" set by the Metropolitan police's department for professional standards. He threw away cannabis left in a car rather than booking it in at the police station. He was charged with misfeasance in a public office and sent for trial at the Old Bailey. His team insisted they would no longer turn a blind eye to cannabis or put it "down the drain". They were going to arrest everyone they found with cannabis.

We had a problem. What would be the effect on a community already suspicious of police motives if there was a massive increase in arrests for even the smallest amount of cannabis? The only solution was a formal, officially sanctioned policy for dealing with cannabis informally.

I discussed the idea with my boss, local people and a trusted journalist, who ran the story in the London Evening Standard in March 2001. The ensuing debate came out positively: even sceptics at Scotland Yard could not escape the futility of arresting people for small amounts of cannabis. The Met commissioner, Sir John Stevens, officially sanctioned a pilot scheme in Lambeth to run from July.

The only significant voice of dissent came from a local Conservative councillor who ultimately objected only because it was not being extended across London. A Mori poll showed only 7% of white residents, 10% of black and 7% of Asian residents interviewed opposed the pilot. Street crime in Lambeth has halved and burglary has continued to fall while it is rising in other parts of London, so why all the fuss? Could it be that a number of myths have taken hold?

"It has made children more vulnerable to drugs." The Met has surveyed all primary and secondary head teachers in Lambeth. Primary heads report no instances of intoxicated pupils and secondary heads report, if anything, a fall in drugs incidents. If there seem to be more children smoking, perhaps they are being more blatant about it, or people are more aware of what has been happening in Lambeth for years. The Mori poll showed more than 80% in favour of the way the pilot deals with young people. No one wants their child to get a criminal record over cannabis. Children at risk may be a perception rather than a reality.

"It has attracted more drug users and dealers into Lambeth." The Met has looked at the addresses of all those arrested for drugs offences during the pilot. This shows a decreasing percentage of people from outside Lambeth being arrested. Cannabis and other drugs are so easily available in all parts of London, who would want to come to Brixton for them? Particularly when you consider the way Brixton is portrayed in the media as some kind of dangerous, lawless wasteland (another gross exaggeration). Drug tourism appears to be the expectation rather than the reality.

"No matter where they come from, there have been more drugs arrests since the pilot began." Thank goodness! The increased arrests must be for class A drugs like heroin and crack cocaine, or for dealing. An increase in drugs arrests is more likely to be the result of more police effort, focusing on class A possession and drug dealing, rather than more drug users.

"Whatever the results, people think cannabis is legal." We tried to explain that the pilot was not a change in the law but a change that allowed officers to use their discretion. We tried to explain that cannabis was more likely to be confiscated than before. We tried to explain that dealing cannabis was not part of the scheme. So why is there so much confusion?

The home secretary is minded to reclassify cannabis from a class B to a class C drug. All the responsible agencies say it is in the wrong category in terms of the harm that it causes. If cannabis were reclassified, people could still be prosecuted for possession and receive a maximum two-year sentence. Dealing in the drug would carry a five-year maximum term. Yet even on Sunday a broadsheet newspaper announced: "Cannabis to be 'legalised' within year." No wonder people are confused.

· Brian Paddick has been moved from his post as Lambeth commander to Scotland Yard pending the outcome of an inquiry into allegations about his private life.comment@theguardian.com